1/* Copyright (c) 2016 Sargun Dhillon <sargun@sargun.me> 2 * 3 * This program is free software; you can redistribute it and/or 4 * modify it under the terms of version 2 of the GNU General Public 5 * License as published by the Free Software Foundation. 6 */ 7#include "vmlinux.h" 8#include <string.h> 9#include <linux/version.h> 10#include <bpf/bpf_helpers.h> 11#include <bpf/bpf_tracing.h> 12#include <bpf/bpf_core_read.h> 13 14struct { 15 __uint(type, BPF_MAP_TYPE_HASH); 16 __type(key, struct sockaddr_in); 17 __type(value, struct sockaddr_in); 18 __uint(max_entries, 256); 19} dnat_map SEC(".maps"); 20 21/* kprobe is NOT a stable ABI 22 * kernel functions can be removed, renamed or completely change semantics. 23 * Number of arguments and their positions can change, etc. 24 * In such case this bpf+kprobe example will no longer be meaningful 25 * 26 * This example sits on a syscall, and the syscall ABI is relatively stable 27 * of course, across platforms, and over time, the ABI may change. 28 */ 29SEC("ksyscall/connect") 30int BPF_KSYSCALL(bpf_prog1, int fd, struct sockaddr_in *uservaddr, 31 int addrlen) 32{ 33 struct sockaddr_in new_addr, orig_addr = {}; 34 struct sockaddr_in *mapped_addr; 35 36 if (addrlen > sizeof(orig_addr)) 37 return 0; 38 39 if (bpf_probe_read_user(&orig_addr, sizeof(orig_addr), uservaddr) != 0) 40 return 0; 41 42 mapped_addr = bpf_map_lookup_elem(&dnat_map, &orig_addr); 43 if (mapped_addr != NULL) { 44 memcpy(&new_addr, mapped_addr, sizeof(new_addr)); 45 bpf_probe_write_user(uservaddr, &new_addr, 46 sizeof(new_addr)); 47 } 48 return 0; 49} 50 51char _license[] SEC("license") = "GPL"; 52u32 _version SEC("version") = LINUX_VERSION_CODE; 53